An example of a vehicle that may advantageously use such a closed circuit television system is a tractor-trailer in which the driver sits inside the tractor cab to one side of the vehicle, commonly to the left side. In the absence of the vehicle being equipped with such a closed circuit television system, the driver will typically not enjoy a full field of view either directly to the rear or to the opposite side from where he or she is seated (i.e., to the right side when the driver's seat is on the left side), even assuming that the vehicle is equipped with the usual mirrors. The obstruction of these views is due largely to the presence of the trailer behind the tractor and to the fact that the driver sits to one side of the cab. Equipping such a tractor-trailer with a closed circuit television system having strategically positioned video cameras can substantially widen the driver's fields of view to the rear of the vehicle and to the opposite side from where he or she is seated.
One presently commercially available closed circuit television system for a tractor-trailer comprises plural video cameras, one of which observes a field of view to the rear and another of which observes a field of view to the opposite side from where the driver is seated. These two cameras are coupled via respective video cables with respective video input ports of a video switch that has a video output port coupled via a video cable with a video input port of a video monitor inside the cab where the monitor's screen can be conveniently viewed by the driver. The monitor comprises certain external controls, one of which is an on-off switch for turning the monitor screen on and off, and another of which is a mode switch for selecting either a manual or an automatic mode of operation. The video switch comprises certain external controls, including a mode switch for selecting either a manual or an automatic mode of operation and port-enabling switches associated with the respective video input ports to which the cameras are respectively coupled for selectively enabling each respective port. In addition to the video switch's connections with the cameras and to the connection of the monitor with the video switch, both the monitor and video switch have connections with the vehicle's D.C. electrical system. These connections are to the vehicle's D.C. power for supplying D.C. power and to the vehicle's back-up light switch for sensing when the vehicle's transmission is placed in reverse. Typically, the commercially available system is installed to allow the driver to select the view from any particular camera, except that when the vehicle transmission is placed in reverse gear, as sensed by actuation of the vehicle's back-up light switch that operates the vehicle's back-up lights, the rear view camera overrides any other camera selected for display so that the rear field of view is thus automatically forced onto the monitor whenever the vehicle is placed in reverse.
One tractor-trailer fleet operator has specified certain additional criteria for further automated operation of such a closed circuit television system that will force, or exclude, certain displays on, or from, the monitor without driver involvement, depending upon not only gear selection, but also upon turn signal and hazard warning signal actuation. The commercially available system described above is incapable of meeting these additional criteria without modification.
The present invention relates to a circuit for accomplishing such further automated operation without modification of the components of the commercially available closed circuit television system described above. Briefly, the invention satisfies the specified criteria in a cost-effective manner by a modification that, in a presently preferred embodiment, involves the addition of only two relays, two diodes, and related wiring connections. In the case of vehicles already in service, the modification can be made by tying into existing wiring harnesses. In the case of new vehicles, the modifications can be built into the vehicle wiring as original equipment at the factory, allowing the closed circuit television system to be installed either at the factory where the vehicle is built, or later by the customer.
The invention enables the following operations to be automatically accomplished. 1) The rear video camera will continue to be actively connected to the monitor to the exclusion of any other video camera whenever the vehicle is placed in reverse gear regardless of whether or not a hazard warning or turn signal is being given. 2) The video camera on the side opposite the driver will be actively connected to the video monitor to the exclusion of any other video camera when the turn signal for that opposite side is being given to signal a turn toward that side, provided that neither reverse gear nor the hazard warning signal is being selected at the same time as that turn signal. 3) The video camera on the side opposite the driver will be prevented from being actively connected to the monitor whenever the hazard warning signal is being given. In this way, the monitor will, for a vehicle where the driver sits on the left side of the cab: 1) be forced to display the rear field of view when the vehicle is backing up; 2) be forced to display the right field of view when the vehicle is making a forward right turn and the hazard warning signal is not being concurrently given; and 3) be incapable of displaying the right field of view whenever a hazard warning signal is being given.
The foregoing, along with further features, advantages, and benefits of the invention, will be seen in the ensuing description and claims which should be considered in conjunction with the drawing that accompanies this disclosure as an exemplary presently preferred embodiment of the invention in accordance with the best mode contemplated for carrying out the invention at this time.